Closebutton(X) Graphic Looks Different In Ie And Firefox

[iGuest 3]

We are using a lightbox(Nyromodal - jquery plugin) on our site to open up the details of a person when clicked on a link (picture/name of a person). But the CloseButton('X') graphic looks slightly different on Firefox and IE6(looks the same as Firefox on IE8). Is there any way that I can modify a setting for it to look the same in all browsers? Here is the script we used to create a lightbox:

$j('#ColleagueProfile').attr('href', URL);$j(document).ready(function() { $j('#ColleagueProfile').nyroModalManual({width:625,height:505,zIndexStart:10000}); });

Thanks a lot in advance!!